Vacuum sealing process of a mems package

ABSTRACT

A vacuum sealing process of a micro-electrical-mechanical-system (MEMS) package is provided. Solder is applied to the rimmed bottom of a lid for the package. A micro-electro-mechanical system (MEMS) device is attached to a substrate for the package. Solder is applied to a lipped top of the substrate. The lid and the substrate are sealed in an elevated temperature and vacuum environment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/532,303, filed Sep. 8, 2011, which is incorporated herein by reference.

FIELD OF INVENTION

This invention relates a method to vacuum seal a package for a micro-electro-mechanical system (MEMS).

DESCRIPTION OF RELATED ART

A micro-electro-mechanical systems (MEMS) is a device of small mechanical devices driven by electricity. The MEMS is often enclosed in a package that protects it from the environment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows an exemplary micro-electro-mechanical system (MEMS) package;

FIG. 2 shows a flowchart of an exemplary method to vacuum seal the MEMS package of FIG. 1;

FIG. 3 shows a rimless lid bottom of the package of FIG. 1; and

FIG. 4 shows a lipless substrate top of the package of FIG. 1, all arranged in accordance with embodiments of the invention.

Use of the same reference numbers in different figures indicates similar or identical elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a micro-electro-mechanical system (MEMS) package 100 in one or more embodiments of the present disclosure. Package 100 includes a package lid 200 with a transparent (e.g., glass) window 210, and a package substrate 300 with a MEMS device 400. Lid 200 may have a rimmed bottom 260 with a lower surface 261 and a side surface 262. Alternatively lid 200 has a bottom 702 without a rim as shown in FIG. 3. Referring back to FIG. 1, substrate 300 has a lipped top 310 with a top surface 311 and a side surface 312. Alternatively substrate 300 has a top 704 without a lip as shown in FIG. 4.

Referring back to FIG. 1, substrate 300 may be made of a ceramic material. The interior of substrate 300 may be plated with a metal such as gold to form bond pads for MEMS device 400. The bond pads may be connected by vias to external pads or pins of substrate 300. Surfaces 311 and 312 of lipped top 310 may also be plated with a metal such as gold. MEMS device 400 includes a stationary part 410 and a moving part 420. When substrate 300 has a lipless top 704 (FIG. 4), the top maybe plated with a metal rectangular ring 706 (FIG. 4) that matches rimmed bottom 260 or rimless bottom 702 (FIG. 3). MEMS device 400 may further include a glass substrate (not shown) supporting stationary part 410 and moving part 420. MEMS device 400 may be connected by bonding wires 510 and 520 to substrate 300. MEMS device 400 may be a scanning mirror.

FIG. 2 is a flowchart of a method 600 to vacuum seal package 100 in one or more embodiments of the present disclosure. Method 600 may comprise one or more operations, functions or actions as illustrated by one or more blocks. Although the blocks are illustrated in a sequential order to demonstrate method 600, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or eliminated based upon the desired implementation.

In block 610, lid 200 is prepared. Lid 200 may be first visually inspected, cleaned, and dried. Lid 200 may be cleaned using ultrasound in an ultrasonic cleaning machine available from ACE Ultimate Co., Ltd. of Thailand. Block 610 may include blocks 612, 614, 616, and 618.

In block 612, a flux is applied on lower surface 261 of rimmed bottom 260 or rimless bottom 702 of lid 200. The flux may be Senju Sparkle Flux ES-1061 from Senju Metal Industry Co., Ltd. of Tokyo, Japan. Block 612 may be followed by block 614.

In block 614, a solder is applied on lower surface 261 of rimmed bottom 260 or rimless bottom 702 of lid 200. The solder may be Senju RMA-98 SUPER P3M705 0.4MM (250G) from Senju Metal Industry Co., Ltd. of Tokyo, Japan. Alternatively the solder may include flux material so block 612 may be skipped. Block 614 may be followed by block 616.

In block 616, a flux is applied on side surface 262 of rimmed bottom 260 or rimless bottom 702 of lid 200. The flux may be the same as the one used in block 612. Block 616 may be followed by block 618.

In block 618, a solder is applied on side surface 262 of rimmed bottom 260 or rimless bottom 702 of lid 200. The solder may be the same as the one used in block 614. Alternatively the solder may include flux material so block 616 may be skipped. Lid 200 may then be cleaned twice with ultrasound and air dried between the cleaning Block 618 may be followed by block 620.

In block 620, substrate 300 is prepared. Substrate 300 may be first visually inspected, cleaned with ultrasound, and dried. Block 620 may include blocks 622, 624, and 626.

In block 622, MEMS device 400 is attached to substrate 300. MEMS device 400 may be attached by an adhesive. Block 622 may be followed by block 624.

In block 624, bonding wires 510 and 520 are applied to electrically connect MEMS device 400 and substrate 300. Block 624 may be followed by block 626.

In block 626, a solder is applied on surfaces 311 and 312 on lipped top 310 or on metal rectangular ring 706 on lipless top 704 of substrate 300. The solder may be the same as the one used in block 614. A flux may be first applied to surfaces 311 and 312 or metal rectangular ring 706 before the solder. Alternatively the solder may include flux material. Note that step 626 may precede steps 622 and 624. Block 626 may be followed by block 630.

In block 630, package 100 is vacuum sealed. Lid 200 and substrate 300 may be first visually inspected, cleaned, and dried. Lid 200 and substrate 300 may be cleaned with alcohol. Block 630 may include blocks 632, 634, and 636.

In block 632, lid 200 and substrate 300 are aligned so rimmed bottom 260 of lid 200 fits around lipped top 310 of substrate 300 with similar spacing on all fours sides. Alternatively rimless bottom 702 fits around lipped top 310 or aligns with metal rectangular ring 706 on lipless top 704, or rimmed bottom 260 aligns with metal rectangular ring 706 on lipless top 704. Block 632 may be followed by block 634.

In block 634, pressure is applied from the top of lid 200 against substrate 300. For example, a weight is placed on the top of lid 200 to press it down against substrate 300 when the solder melts. Block 634 may be followed by block 636.

In block 636, lid 200 and substrate 300 are sealed in an elevated temperature and vacuum environment so package 100 is vacuum sealed when the solder melts and later solidifies. For example, a hot plate in a vacuum chamber may be used, the vacuum chamber's pressure may be set to 1 Ton, the hot plate may be preheated to 265 degrees ° C. for about 25 minutes, package 100 may be placed in the vacuum chamber and the hot plate may then run for 25 minutes, and package 100 may be allowed to cool for one hour. Package 100 may be vibrated to facilitate the solder bonding between lid 200 and substrate 300.

Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. Numerous embodiments are encompassed by the following claims. 

1: A method to vacuum seal a micro-electro-mechanical system (MEMS) package, comprising: applying a solder to a bottom of a lid for the package; attaching a MEMS device to a substrate for the package; applying the solder to a top of the substrate; aligning the lid and the substrate by fitting the bottom of the lid around the top of the substrate; applying pressure to the lid against the substrate; and sealing the lid and the substrate at elevated temperature and under vacuum. 2: The method of claim 1, wherein the bottom of the lid comprises a rimmed bottom. 3: The method of claim 2, wherein applying a solder to a bottom of a lid for the package comprises applying the solder to lower and side surfaces of the rimmed bottom. 4: The method of claim 1, wherein the top of the substrate comprises a metal rectangular ring. 5: The method of claim 4, wherein applying the solder to a top of the substrate comprises applying the solder onto the metal rectangular ring. 6: The method of claim 1, wherein the bottom of the lid comprises a rimless bottom. 7: The method of claim 6, wherein applying a solder to a bottom of a lid for the package comprises applying the solder to lower and side surfaces of the rimless bottom. 8: The method of claim 1, wherein the top of the substrate comprises a lipped top. 9: The method of claim 8, wherein applying the solder to a top of the substrate comprises applying the solder to top and side surfaces of the lipped top. 10: The method of claim 1, further comprising: applying a flux to the bottom of the lid. 11: The method of claim 10, further comprising: applying the flux to the top of the substrate. 12: The method of claim 1, wherein the solder includes a flux. 13: The method of claim 1, wherein sealing the lid and the substrate at elevated temperature and under vacuum comprises heating the package at 265° C. under 1 Torr. 14: The method of claim 13, wherein sealing the lid and the substrate at elevated temperature and under vacuum further comprises vibrating the package. 15: The method of claim 1, further comprising wire bonding the MEMS device and the substrate. 